Apparatus for producing or enhancing a perceived sensation of motion

ABSTRACT

A motion simulator in the form of a seat ( 11 ) comprising a seat support frame ( 12 ) including a seat back ( 13 ), in which a seat pan ( 19 ) is movably mounted with respect to the seat support frame ( 12 ) via motion actuators ( 20, 21, 22 ) which impart to the seat pan ( 19 ) motion with respect to the seat support frame ( 12 ) with at least three degrees of freedom including sway, and control means ( 34 ) for determining the motion of the actuators ( 20, 21, 22 ) to move the seat pan ( 19 ). Many cues involve moving the seat pan in the opposite sense from the simulated direction of movement.

This invention relates to apparatus for producing or enhancing aperceived sensation of motion as used, for example, in apparatus such asflight simulators which are used in the training of pilots. Theapparatus of the present invention can, however, be used for othertraining purposes, and also for recreational purposes. In use of theapparatus of the invention a seated user is given the subjectiveimpression of movement as a result of simultaneous visual and/or audiostimulation together with motion “cues”. In known such apparatus, thesubjective impression of movement is achieved either by pivotal movementof the entire seat or by varying the pressure and/or hardness of anarray of pressure pads arranged on the seat and which support the userwith varying degrees of support pressure in different parts of theuser's anatomy, or a combination of the two.

In the design of such seats, attention has mostly been directed to themotions of pitch, roll and heave (vertical translation), with littleattention, if any, being paid to the other possible motions experiencedby a body moving in three dimensional space, namely sway (lateraltranslation), surge (translation along a longitudinal axis) and yaw.Attention has also mostly been directed to motion simulators addressedto gross stimulation of the visceral and haptic-somatic sensory systemsto engender the sensation of movement in the user. However the motionsto which such apparatus can be subject is limited in the duration ofsome of the cues that it can generate. This is because a motion base isdesigned to apply a real acceleration to the occupant that correspondswith the computed acceleration of the virtual vehicle. Realacceleration, of course, results in a real velocity that in turn resultsin a real movement of the simulator motion base. Since the rams have afinite stroke, the possible displacement of the motion base is stronglylimited, which means that the accelerations can only be applied for ashort period—fractions of a second. What is more, it is necessary toapply a reverse acceleration immediately afterwards, so as to bring themechanism to a halt before the rams crash into their end stops. Then themachine has to be returned to its starting position to await the nextmotion cue demand. The acceleration cues are therefore limited toshort-duration “onset cues” and they are followed by reverse motion“wipe-outs”.

One improvement over such known systems is described in U.S. Pat. No.4,321,044 of G J Kron, which relates to a so-called “G-seat” having aseparate seat and backrest, both of which are provided with an array ofpressure pads, the internal pressure of which can be varied individuallyand in accordance with a predetermined program, to vary the degree ofsupport given to different regions of the body of a user seated in theG-seat. The seat pan is pivotally mounted on a motion plate pivotallymounted on the frame and driven by hydraulic rams to provide the pitchmotions; the seat pan is also pivoted on the motion plate to achieve anapproximation of roll motion and is capable of longitudinal motion alongthe seat plate, which is traditionally defined as being the direction offore/aft travel, under the action of a fourth ram. A restraining devicedetermines the pitch and roll axes at fixed locations and any othermovement, in particular sway, that is transverse translational motion ofthe seat pan is specifically prevented by this stabiliser. A similarthree point drive is provided to the backrest to provide pitch, roll andsurge motions, but in this case with both lateral and verticalstabilisers to prevent both sway and heave, that is lateral movement ofthe backrest or translation of the backrest in a vertical direction.

An important element creating a perception of motion in a motionsimulator is the scrubbing effect simulating relative movement of theoccupant in relation to the seat. The importance of such cueing motionsis recognised in U.S. Pat. No. 4,030,207 in. which provision is made forlinear displacement of the seat cushion surface along either of the twoorthogonal axes, such displacement taking place in the plane of thecushion surface by physically displacing the surface covering of theseat with respect to the seat itself whereby to generate what may bereferred to as skin tension/contraction cues in the user.

The present invention is directed to apparatus for producing orenhancing a perceived sensation of motion in which the motion to besensed by the user is represented by clues or cues which are producedwithout gross movement of the seat itself but rather by subtle relativemovements of some part or parts of the seat with respect to another orothers, in particular by movements of the seat pan upon which the useris seated, relative to the frame of the seat which is fixed. The actualmovement of the seat is not necessarily in a direction intuitivelyassociated with the sensation of movement intended to be perceived bythe user. As will be described in more detail below the seat pan may besimultaneously subjected to one or more motions selected from up to fiveof the “natural” degrees of freedom namely pitch, roll, sway, surge andheave. Although the user may be caused to perceive yaw motion this isnot created by displacements about the yaw axis but rather bycombinations of other displacements. The motion to be perceived by theuser in the context of this invention may also be selected from anycombination of surge, sway, yaw, pitch, roll and heave by means of cuesgiven from very small relative movements of he seat as will be describedin more detail below.

According to one aspect of the invention apparatus for producing orenhancing a perceived sensation of motion in the form of a seatcomprising a seat support frame including a seat back, is characterisedin that a seat pan is movably mounted with respect to the seat supportframe via motion actuators which impart to the seat pan motion withrespect to the seat support frame with at least three degrees offreedom, and control means for determining the motion of the actuatorsto move the seat pan with respect to the frame to provide the simulatedmotion.

The perception or enhanced perception of motion is achieved by movingjust the seat pan in such a way as to vary the skin pressure between theuser and those parts of the seat contacted thereby.

As used in this specification the term “seat pan” will be understood torefer to the platform or squab on which a seated person actually sitsregardless of whether this is padded or unpadded. Likewise, whenreferring to the “general plane” of the seat pan it will be understoodthat this refers to a plane in which the majority although notnecessarily the entirety of the seat pan lies.

Also in accordance with this invention there is provided an apparatusfor producing or enhancing a perceived sensation of motion comprising asupport platform having five or six degrees of freedom, that is to sayrotational freedom about each of two or three orthogonal axes, andtranslational freedom along each of these axes.

When a person is seated in a moving vehicle (car, boat, plane etc,) theoccupant of the seat always moves within the seat in the oppositedirection from that of the motion of the seat itself. This is because,if the vehicle changes course in any dimension, the inertia of theoccupant acts to make him/her continue on the original course—and as aresult the occupant is pressed against the opposite seat surface. It istherefore possible to design a completely new form of motion cueingsystem in which the seat occupant is moved by the seat pan a fraction ofan inch in the opposite direction to that of the virtual vehicle motion.So the occupant is pressed against the appropriate surface of the seat,as would be the case in reality. Of course, there are limitations to thetechnique in the case of heave accelerations, but that is common to allother forms of motion cueing system.

In another aspect, the present invention provides apparatus comprising asupport platform constituting or mounting a seat pan, the said platformbeing freely movable, over a limited range of motion with at least fivedegrees of freedom with respect to a seat frame. The seat frame may bestatic or may be itself mounted on a motion base to provide grosspositional changes as well as the motion cues from the motion of theseat pan which effectively “floats” in relation to the seat frame.

Motion simulation is achieved, in accordance with the present invention,without the need for pressure pads located on the seat pan or on thebackrest, and without varying the hardness of the support surface,and/or without varying the tension in a lap belt fitted to secure theuser in the seat, although any or all of these may be added to reinforcethe simulation if considered appropriate to particular circumstances.

Embodiments of the invention may be so formed that, in order to permithorizontal movement of the seat pan, that is movement within the planeof the pan when lying at rest, no separate dead load carrying means orlateral restraining means are required. In such embodiments theactuators provide the sole support for the motion plate on which theseat pan is carried as well as providing the pitch, roll, sway, surgeand heave motions (and yaw if provided). For this purpose the actuatorsmay be combined electromagnetic linear actuators with fluid pressuresupport or backup. Suitable such actuators are described in, for exampleWO98/37615. Preferably the sole support for the motion platform isprovided by the actuators. These actuators are connected to the motionplate at the three corners of a triangle, preferably an equilateraltriangle. In one embodiment they may be substantially verticallyoriented between the support plate and the motion plate, although inorder to permit the extra degrees of freedom to the motion plate forsurge and sway motion universal linkages or joints are needed at eachend of each actuator, and further actuators for providing these motionsmay be provided. Alternatively, the actuators may be inclined to oneanother in a configuration resembling a truncated tetrahedron. As afurther alternative, six actuators in a so-called “Stewart platform”configuration may be provided to give up to six degrees of freedom. Theconfiguration of the actuators used to support and drive the motionplate relative to the fixed support frame may be such as to provide anaxis of rotation parallel to and adjacent the leading edge of the seatpan for a single actuator; for example the front of the motion plate maybe supported by two actuators equi-spaced on opposite sides of thelongitudinal axis whilst the rear (front and rear in this context, andelsewhere in the present description, being relative to the direction inwhich the user faces when seated in the simulator) is supported by asingle actuator.

In one embodiment of the present invention, the motion plate to whichthe seat pan is mounted, or which itself constitutes the seat pan, or asection thereof, may be provided with up to three of its degrees offreedom namely surge, sway and yaw by means of actuators operating inthe general plane of the motion plate. The three actuators may comprisethree further preferably electromagnetic rams each operating along arespective line of action. Alternatively six actuators, preferablyelectromagnetic rams located in pairs to work in opposite directionalong each of these three lines of action may be provided. These rams,(three or six as the case may be) operate co-operatively to drive themotion plate linearly (or in rotation for yaw), and in the plane of theplate, either along the longitudinal or transverse directions, or bothsimultaneously. Movement of the seat pan along the longitudinaldirection serves to cue the perceived motions in the user of surge(forward movement or acceleration) or negative surge (braking), theperceived motion being opposite the actual motion of the seat pan, thatis forward movement of the seat pan along the longitudinal direction isperceived by the user as negative surge, that is rearward movement orbraking, whilst movement of the seat pan transversely of thelongitudinal direction serves to cue motions perceived by the user assway, the perceived or apparent direction of movement likewise beingopposite that of the actual movement of the seat pan transverse thelongitudinal direction.

A particular advantage of the arrangement of this invention, besidesadding surge and sway capability to the motion simulator, is that it canbe used to provide strong and accurate simulation of a vibrationalenvironment. In general this has not been possible or practical in thepast. Vibrational motion is possible largely due to the use ofelectromagnetic actuators as these have a wide bandwidth of mechanicalresponse to the stimulating signals.

In the embodiments described above, the position of the seat pan on themotion plate is preferably such that the centre of mass of the user,that is the person seated on the seat pan, is at least substantiallydirectly above the centroid of the triangle of the connection points ofthe actuators with the motion platform.

It is possible, within the principles of the present invention, toprovide the motion platform with a further degree of freedom (for whicha further drive mechanism may be provided (unless a six actuator Stewartplatform configuration is used), this being that of rotation about anaxis perpendicular to the plane of the motion plate. This final degreeof freedom rotates the motion plate to a limited extent about asubstantially vertical axis thereby to cue a perceived sensation of yawin the user. As mentioned above the yaw sensation can be cued by meansof a combination of pitch and roll movements with a possiblecontribution from sway. The use of the true yaw motion of the seat panmay also contribute to this but can be used to reinforce other cues aswell. All six of the motions capable of being experienced by a bodymoving in three-dimensional space, that is any or all of pitch, roll,heave, surge, sway and yaw can all be simulated with the apparatus ofthe invention.

Various opportunities exist for the location of the yaw axis. Generally,the yaw axis will be aligned on the longitudinal axis, and within theequilateral triangle formed by the connection of the actuators on whichthe motion plate is carried, although there may be occasions when theyaw axis is set to one side or the other of the X axis itself forspecial purposes. Likewise the yaw axis will generally be set either atthe point of intersection of the longitudinal and transverse axes or soas to pass substantially directly through the centre of mass of a userseated on the seat pan, although, as mentioned, the two are preferablycoincident. Other possibilities exist, however, such as positioning theyaw axis in front of or behind the centre of mass of the user. This hasapplication where the apparatus is used for special purposes such as foran entertainment simulator rather than for a training simulator.

Generally the apparatus of the present invention will have a seat backor backrest as well as a seat pan. As is the normal practice both willusually be upholstered for the comfort of the user. Either or both mayadditionally be provided with pressure pads and/or hardness modulators,although a primary objective of the invention is to provide a motionsimulator which is effective without them. Where present, such pressurepads and/or hardness modulators may be of any known design.

In the motion simulator of the present invention the seat pan isentirely independent of the seat back or backrest and there is no needfor motion of the seat back or backrest with respect to a stationaryframe of reference in order to achieve the motions simulation.

Generally the apparatus of the invention will comprises an adjustableseat belt for the user. As mentioned above, a separate drive fortensioning and releasing the seat belt is not needed in order to givethe motion cues, but of course the seat belt may be positively driven inassociation with movements of the seat if required. One of theadvantages of the present invention over the prior art is that, in thepresent invention, such tensioning variation is not necessary, the seatbelt need not be tensioned other than by adjustment for fitting.

Where reference is made in this specification and claims to theperception of motion by the user, such term is to be taken as includingenhancement of that perception, that is the perception itself may beinitiated or cued by other means, the present invention serving toenhance the already initiated perception.

Embodiments of the present invention will now be more particularlydescribed, by way of example, with reference to the accompanyingdrawings, in which:

FIG. 1 is a schematic diagram illustrating a simulator seat formed asone embodiment of the present invention;

FIG. 2 is a schematic side view of the embodiment of FIG. 1 in a firstoperating configuration;

FIG. 3 is a corresponding schematic side view of the embodiment of FIG.1 showing the device in an alternative configuration;

FIG. 4 is a schematic diagram illustrating an alternative embodiment ofthe invention;

FIG. 5 is a perspective view of a further alternative embodiment of theinvention; and

FIG. 6 is an axial sectional view of an electromagnetic ram suitable foruse in embodiments of the invention.

Referring now to the drawings, FIG. 1 illustrates a simulator seatgenerally indicated 11 comprising a fixed frame 12 having a seat back13, left and right arm frames 14, 15, legs 16, 17 mounted on a fixedplatform 18. All these components are securely and rigidly fixedtogether so that no relative movement between any of them can takeplace.

Between and beneath the arms 14, 15 is located a seat squab or seat pan19, being that component on which an occupant is seated when occupyingthe simulator seat. The seat pan 19 takes the entire weight of theseated occupant. The seat pan 19 is carried by three linear actuators20, 21, 22 which are preferably of electromagnetic type as described inthe inventor's earlier PCT application WO98/37615. The linear actuatordescribed in this earlier document produces a controlledaxially-directed force and comprises two main relatively movable membersadapted to slide telescopically one within the other, a plurality ofannular coils are fixed to at least a portion of the axial length of oneof the relatively movable members, and means for generatingcircumferential electric currents in the annular coils. The otherrelatively movable member has means for producing a plurality ofmagnetic fluxes the polarity of which alternates along at least aportion thereof. The current generating means act to vary either one ormore of the frequency, the phase or the amplitude of the electriccurrents in the coils so as to cause the electric currents and magneticfluxes to interact and to provide a force tending to cause relativemotion between the members which each have an open end and a closed endand are fitted one within the other to define an enclosed volume betweenthem. This enclosed volume is filled with a fluid under pressure,preferably gas, which enables the actuator to support a static loadwithout energisation of the coils.

In the context of this application, therefore, each of the actuators 20,21, 22 contributes to supporting the load of a user on the seat pan 19which rests on a movable platform 24 to which the actuators 20, 21, 22are pivotally connected by universal joints 25, 26, 27 respectively. Attheir lower ends the actuators 20, 21, 22 are connected to the supportplatform again by respective universal joints 28, 29, 30. The movableplatform 24, and thus the seat pan 19, is carried solely by theactuators 20, 21, 22 and is therefore free to “float” in relation to tiefixed frame 12. For this purpose the platform 24 is made two dimensionsslightly smaller than the available space within the frame 12 so that itis free to move, albeit over a limited range, horizontally within itsown plane as well vertically. Tilting motions about either alongitudinal or a transverse axis may also be made as will be describedin more detail hereinafter below. In this context the longitudinal axis,represented by the arrow X in FIG. 1, coincides with the four and aftaxis of the seat 11, with positive displacement in the X direction beingrepresented by forward movement or movement in the direction in whichthe occupant faces. The transverse axis, represented by the line Y-Y inFIG. 1, lies orthogonally to the longitudinal axis and in the samehorizontal plane. The third axis, namely the Z axis represents thevertical direction as illustrated by the arrow Z in FIG. 1, and isorthogonal to the plane defined by the XY axis in the usual cartesianconvention.

Control signals to the actuators 20, 21, 22 are applied via lines 31,32, 33 from a control unit 34 which itself receives signals from ademand unit 35 which may be a manual control unit for real-time controlof the seat, or may be a recorded program relating to, for example, theimages displayed to the user on a screen (not shown) facing the seat 11or a virtual-reality headset (again not shown) which the user may wear.

The art of simulating motion has been developed over a number of yearsas described in the preamble to this specification: one of thecontinuing problems, however, is that of the limited range of theactuators which provide the motion simulation. In early simulators wherethe motion is actually reproduced, rather than simulated, accelerationupward, for example, is represented by raising the entire seatstructure, rolling to the left and right is simulated by correspondingsuch motions. However, such so-called “gross movement” simulators couldnot provide a representation of sustained acceleration in one directionsince the actuators would reach the end of their travel long before thedesired simulation came to an end. For this purpose the so-called g-seatwas developed, which provides motion queues rather than gross motionwhich, in combination with the images represented to the occupant of theseat, provided a psychological rather than a real representation of themotion. Increasingly complex and sophisticated systems have beendeveloped in order to convince the occupant that the simulated motion isin fact taking place, including means for moving the seat pan and theseat back in relation to one another, skin “scrubbing” arrangements formoving the surface of the seat pan and and/or the seat back in the planeof contact with the user to simulate the “tug” experienced by the userin a real-life situation when his or her body weight is caused to shiftin relation to the seat itself, and various inflatable pressure pads forvarying the pressure experienced by different parts of the seatoccupant's anatomy again to simulate the hardness variations which areexperienced in different attitudes and with different accelerationpatterns.

The present invention is based on the realisation that suchpsychological motion cues are not all necessary in order to provide arealistic representation of the motion, and that by simply displacingthe occupant in relation to the seat frame by moving him or her by meansof motion of the seat pan a very credible simulation of motion,especially sustained acceleration, can be achieved without the need forsuch complex structures as have been developed. For this purpose theseat pan can be made to be capable of movement over a greater range inrelation to the frame than in conventional g-seats, although not oversuch a great range as in gross motion simulators, and the “scrubbing”action between the occupant and the parts of the seat with which he orshe comes into contact can be achieved by effecting real scrubbingmotions of the occupant against the static parts of the seat by movingthe occupant rather than the seat. It is anticipated, however, that inorder to apply the required skin pressure variations to simulatesustained acceleration only very small movements will be actuallyrequired for the majority of circumstances.

Thus, for example, if it is desired to simulate vertical acceleration inthe Z direction this is achieved by shortening each of the actuators 20,21, 22 by the same amount to cause the seat pan 19 to descend withrespect to the seat frame 12 thereby giving the occupant the impressionthat the seat frame is rising with respect to a frame of referencecentred on the occupant himself, which is the same physical sensation asthat occurring during real vertical acceleration as the inertia of theoccupant causes him or her to be pressed down into the seat and thusoccupy a lower position than in steady state conditions. Of course, itis appreciated, that this simulation does not provide the visceralstimulation of acceleration, but in combination with the visual imagespresented at the same time can act to provide a credible simulation. Inthe same way a sustained acceleration to the right, for examplesimulating a long sweeping curve to the right of a motor vehicle, can besimulated simply by rolling the seat pan to the left causing theoccupant to experience greater pressure on the left side from the lefthand seat arm 14, and also experience a slight lateral tug or scrub onthe back again simulating the inertia of the occupant in a realsituation.

In general, as explained above, all simulated motions are represented byactual displacement of the seat pan in the opposite direction of that ofthe motion being simulated, that is the opposite direction from thatwhich the seat as a whole would move in a real displacementcorresponding to that simulated. Positive heave, as mentioned above, issimulated by lowering the seat pan 19 in the negative Z direction andnegative heave, that is deceleration vertically (or downwardacceleration) is represented by elevating the seat pan 19 by extendingthe actuators 20, 21, 22 in relation to the seat frame 12.

The articulation of the ends of the actuators 20, 21, 22 to the fixedplatform 18 and to the movable platform 24 on which the seat pan 19 issupported allows a limited translational movement of the seat pan 19 totake place, this being effected by further actuators (not shown) actingbetween the frame 12 and the platform 24 in a horizontal direction,typically parallel to the X and Y axes.

One advantage of mounting the seat pan 19 on a platform 24 which issupported independently of the frame 12, in a manner which can becharacterised as a “floating” mount, lies in the fact that the axisabout which any rotation takes place can be shifted within the area ofthe platform 24, or, indeed, to lie outside the area of the platform 24by suitably controlling the actuators 20, 21, 22. One example of this isillustrated in FIG. 2 and FIG. 3 in which the seat pan 19, the platform24, the left hand front actuator 22 and the rear actuator 20 are shown.It will be appreciated that the preferred configuration of the actuators20, 21, 22 is as shown in FIG. 1 with a lower ends of the actuators 20,21, 22 connected to the fixed platform 18 by articulation couplings 28,29, 30 located at the corners of an equilateral triangle which is thesame size as the equilateral triangle made by the articulated couplings25, 26, 27 by which the upper ends of the actuators 20, 21, 22 areconnected to the platform 24, with the actuators 21, 22 defining thetransverse plane at the front of the platform 24 and the actuator 20controlling the rear of the platform 24. If, in simulating a particularmotion, it is desired to tilt the platform 24 and thus the seat pan 19rearwardly, this can be achieved as illustrated in FIG. 2, by turningthe seat pan 19 about an axis passing through the two articulations 26,27 by maintaining the actuators 21, 22 at an unchanged length andshortening the actuator 20. Lengthening the actuator 20 would cause theseat pan 19 to tilt forwardly about an axis passing through the twoarticulations 26, 27. However, in other circumstances rearward tiltingof the seat pan may more preferably be achieved by maintaining thelength of the rear actuator 20 and extending the front actuators 21, 22,in which case the seat would tilt about a transverse axis passingthrough the articulation 25.

As indicated above, if it were desirable to turn the seat pan 19 aboutan axis outside its own area this could be achieved by extending theactuators 21 and 22 by an amount greater than the actuator 20 such thatthe tilt took place about an axis somewhere to the rear of the seat.This allows a wide variety of simulated motions to take place. Forexample, when simulating vertical acceleration it may be moreappropriate simply to lower the rear of the seat 20 as illustrated inFIG. 2 since the majority of the occupant's weight is communicated tothe seat via the ischial tuberosities in line with the hip joints.Relatively little of the occupant's inertia affects the front of theseat However, when simulated acceleration or deceleration in afour-and-aft direction it may be more appropriate to raise or lower thefront of the seat leaving the rear of the seat at a fixed height inorder to avoid raising or lowering the occupant's line of sight andthereby increasing the perception intended by the simulation.

FIG. 4 illustrates an alternative configuration in which the platform 24is mounted on six actuators mounted in pairs connected to the samearticulation points 25, 26, 27 as the individual actuators 20, 21, 22 ofthe embodiment of FIG. 1, the actuators being identified as left andright components 20L, 20R, 21L, 21R, 22L, 22R. This known platformconfiguration enables the platform 24 to move with six degrees offreedom without requiring any additional actuators, and in particularcan cause horizontal translations in the XY plane, rotation about the Zaxis (yaw) as well as the heave, pitch and roll displacements discussedabove in relation to the embodiment of FIG. 1.

It is also possible to combine the present invention with a gross motionsimulator by mounting the fixed platform 18 on a motion base (whichitself may be a stewart platform) having long-reach actuators such thatthe seat frame 12 itself can be caused to perform physical displacementsor rotations within a limited range. Such a structure would provide theadvantage of being able to stimulate both the visceral and hapticsystems simultaneously to achieve a more realistic simulation of motion,especially sustained acceleration.

An advantage of utilising electromagnetic actuators 20, 21, 22 lies inthe frequency response of such devices, which are capable of applying tothe seat pan 19, and thus to the seat's occupant a vibratory motion upto several tens of Hz which is achieved only with difficulty utilisinghydraulic actuators.

The algorithm driving the actuators is preferably formulated so that notonly is the motion to be perceived by a user seated on the seat pan cuedby a brief cueing movement of the seat pan in the opposite direction, sothat the sensation resulting from the tugging or dragging or scrubbingwhich occurs between the user or his clothes and the fixed parts of theseat as the seat pan (and therefore the user) is displaced, results in achange in skin tension or contraction brought about by the scrubbingaction and thus a perception of motion. The algorithms used to drive theactuators should preferably be formulated so as to provide rapid washoutat the end of each movement, especially lateral motion: longitudinalmotion may have a longer washout. This is needed in order to ensureavailability of motion in the same or opposite direction immediatelyafter any given motion.

The configuration of the seat is such that the centre of mass of aperson seated on the seat pan, and which for practical purposes can beequated with the position of the navel, is directly above the centroidof motion of the seat pan 19. This may or may not coincide with theZ-axis.

Referring now to the embodiment of FIG. 5, a motion simulator generallyindicated 30 has a fixed seat frame 31. The seat frame 31 comprises abase 32 of generally triangular configuration at the apices of which arethree upstanding bosses 33 through which pass respective pivot pinscarrying resilient bushes 34 on which are mounted respective pairs oflinear actuators 35, 36; 37, 38 and 39, 40. In fact the actuator 39 isnot visible in FIG. 5 as it is masked by the actuator 40. Each of theactuators 35, 36; 37, 38; 39, 40 is connected at its lower end to theresilient bushes 34 on the support bosses 33, and pivotally connected atits upper end to a seat support plate 41 of triangular shape on which ismounted a seat pan generally indicated 42 comprising a rigid seat plate43 and a relatively firm cushion element 44. The resilient bushes,although cylindrical in shape, out in practice as universal joints oflimited displacement, and are silent in operation.

The configuration of the linear actuators 35-40 is, in practical terms,comparable to the “Stewart” platform configuration of FIG. 4, but inwhich the triangle of connection points ABC in FIG. 5 is rather smallerthan that illustrated in FIG. 4 so that, with the actuators themselvesbeing of greater transverse thickness and mounted in pairs on the bushes34, each adjacent “V” of the actuators in FIG. 4 is constituted by apair of approximately parallel actuators as shown in FIG. 5. Theactuators 35, 36, for example, have been marked with the letters B and Cto indicate the corresponding connection points B and C of actuators inFIG. 4. As will appreciated, the seat pan 42 is carried on the seatsupport plate 41 solely by the six actuators 35-40, in turn supportedsolely on the base 32.

Upwardly from the base 32 extends a rigid support frame generallyindicated 31 comprising a rear rectangular frame of upright columns 45reinforced by two transverse struts 46, 47. Forwardly from the columns45 project two inclined supports 48, 49 in turn supported by uprightcolumns 50, 51 adjacent their forward ends, the columns 50, 51 being inturn secured to the upright rear frame by rails 52.

A backrest 53 is fixedly supported on the fixed frame 31, by means notshown, and thigh supports 54, 55 are carried by the inclined arms 48,49, and are adjustable by means of screw threaded adjusters 56, 57, 58,59. It will be appreciated that the thigh supports, 54, 55 and thebackrest 53 are all rigid, non-moving parts held stationary by thesupport frame 31 on the base 32 whilst the seat pan 42 is movable, inthe manner described herein above, with respect to these fixedcomponents in order to provide a simulation of motion.

A footrest 60 carried on a projecting arm 61 is likewise secured to thebase 32 and fixed in relation thereto. Electrical leads 62, 63, 64 leadfrom a control panel 65 to the individual actuators 35-40 so that thesecan be caused to extend or contract individually in accordance with thedesired motion.

For use as a training simulator, the controls of the actuators arelinked to a control column 66 by which the user applies demand signalsto the control unit 65 in accordance with external stimuli, such as animage projected on a screen in front of the simulator.

The motion simulation can represent sustained accelerations as well asspecific movements, and the use of electromagnetic actuators allows highfrequency motion, particularly vibrations, to be applied to the seat pan42 thereby providing a more realistic simulation of the real experience.

One of the more difficult motions to provide a credible simulation isthat of “heave” that is vertical acceleration or deceleration in view ofthe limited range of motion of the simulator components in comparisonwith those available to a real vehicle such as an aircraft. This meansthat sustained acceleration must be represented to the user in a waywhich allows his or her brain to interpret the cue as representative ofthis fact without it being possible, naturally, to apply realacceleration. It has been found that a heave simulation of upwardacceleration is more credible if it starts by applying an increasedvertical pressure to the user by elevating the seat pan slightly inrelation to the thigh supports 54, 55 and back 53, and follow this by aslow descent. This gives the user first the sensation of increasedpressure and then the sensation of sinking into the seat in relation tothe back and thigh supports which is reminiscent of the correspondingphysical effect in a real aircraft where the operator is pressed downinto the seat by sustained vertical acceleration.

Likewise, apparent yaw motions can be simulated by a combination ofpitch, roll and lateral translation (sway) applied in a specificsequence which causes the user to develop an apparent sensation ofyawing.

FIG. 6 illustrates the structure of an electromagnetic ram suitable foruse in the embodiment of FIG. 5. The ram, illustrated as the ram 35, hasan outer casing 67 within which are formed and secured thereto aplurality of annular coils 68.

A tubular “piston rod” 69 is attached to an array of annular magnets 70interspaced by tapered pole pieces 71 and carried on a central tubularcarrier 72.

A seal 73 between the cylindrical outer surface of the tubular “pistonrod” 69 and an annular end cap 74 ensures that the interior chamber 75of the actuator is sealed from the outside.

The opposite end the actuator contains a position encoder 76 connectedby an extensible line 77 to the movable magnet array, by a couplinghaving passages 78 which allow communication from the interior of thetubular member 72 to the chamber 79 within the actuator on the oppositeside from the magnet array 71 from the chamber 75. The interior of theactuator, comprising the chamber 75, the interior of the tubular member72 and the chamber 79 contains a gas under pressure so that the actuatoris capable of supporting a load without necessity for the coils 68 to beenergised to displace the magnet array 71. Such actuators are capable ofrapid movement, are silent in operation, and suffer no leakage of oillike hydraulic actuators. They are capable of very rapid displacementsso as to be able to apply not only motion cueing displacements, but alsovibration to the movable seat pan and shock loading to simulate motionswhich cannot be represented bysimulators using less responsiveactuators.

1. Apparatus for producing or enhancing a perceived sensation of motionin the form of a seat comprising a seat support frame including a seatback, characterised in that a seat pan is movable with respect to theseat support frame via motion actuators which impart to the seat panmotion with respect to the seat support frame with at least threedegrees of freedom and control means for determining the motion of theactuators to move the seat pan with respect to the frame to provide thesimulated motion.
 2. Apparatus for producing or enhancing a perceivedsensation of motion according to claim 1, characterised in that, themotion actuators are electromagnetic actuators, preferablyelectromagnetic linear actuators.
 3. Apparatus for producing orenhancing a perceived sensation of motion according to claim 2,characterised in that the seat pan is supported by actuators connectedbetween the seat pan and the seat support frame.
 4. Apparatus forproducing or enhancing a perceived sensation fo motion as claimed inclaim 3, characterised in that the actuators provide the sole supportfor the seat pan.
 5. Apparatus for producing or enhancing a perceivedsensation of motion according to claim 3, characterised in that themotion actuators between the seat support frame and the seat pan arelinear actuators in an arrangement which allows translational movementof the seat pan in the general plane thereof with respect to the seatsupport frame.
 6. A motion simulator according to claim 5 characterisedin that there are six linear motion actuators between the seat supportframe and the seat in a configuration in which the actuators are locatedin pairs each pair acting at a respective corner of the said triangle.7. Apparatus for producing or enhancing a perceived sensation of motionaccording to claims 5 to 6 characterised in that translational movementof the seat pan with respect to the seat support frame is provided byactuators acting between the seat pan and the seat support frame in thegeneral plane of the seat pan.
 8. Apparatus for producing or enhancing aperceived sensation of motion according to any of claims 3 to 6,characterised in that the actuators are connected to the eat pan at thecorners of a triangle and the seat pan is positioned with its front edgeparallel to one of the sides of the said triangle.
 9. Apparatus forproducing or enhancing a perceived sensation of motion according toclaim 8, characterised in that the said triangle is a substantiallyequilateral triangle.
 10. Apparatus for producing or enhancing aperceived sensation of motion according to claim 8 or claim 9,characterised in that the position of the seat pan on the support frameis such that the centre of mass of a user seated on the seat pan issubstantially directly above the centroid of the triangle.
 11. Apparatusfor producing or enhancing a perceived sensation of motion according toany preceding claims, characterised in that the motion actuators betweenthe seat pan and the seat support frame are arranged to providetranslational movement of the seat pan with respect to the seat frame intwo directions orthogonal to one another.
 12. Apparatus for producing orenhancing a perceived sensation of motion according to claim 10,characterised in that the said two orthogonal directions are lateral andlongitudinal.
 13. Apparatus for producing or enhancing a perceivedsensation of motion according to any preceding claim, characterised inthat it further includes a seat belt for a user when seated in thesimulator, the seat belt being adjustable in length to adapt to the userof the simulator and variable in tension during operation of thesimulator.
 14. Apparatus for producing a enhancing a perceived sensationof motion according to any preceding claim, characterised in that thereare provided or also provided means for supporting the static load onthe seat pan separately from the said actuators.
 15. A method ofproducing or enhancing a perceived sensation of motion using a simulatoras claimed in any preceding claim, characterised in that the sensationof motion perceived by the user is achieved or enhanced by cueingsignals produced by movement of the seat pan with respect to the seatframe as permitted by one or more of its degrees of freedom and effectedby operation of respective motion actuators, the direction and durationof movement of the seat pan being such as to simulate the motion to beperceived by the user.
 16. A method of producing or enhancing aperceived sensation of movement according to claim 15, characterised inthat it comprises causing limited, brief movement of the seat pan uponwhich the user is seated, relative to a fixed support, along or about agiven axis, the actual movement of the seat being in a directionopposite to the sensation of movement intended to be perceived by theuser.
 17. A method of producing or enhancing a perceived sensation ofmotion according claim 16 or claim 16, characterised in that, thedisplacement of the seat pan with respect to the seat frame takes placefirst in one directional sense and they in another directional senseduring the same simulated movement.
 18. A method of producing orenhancing a perceived sensation of motion according to claim 17,characterised in that, the simulated perceived sensation is heave andthe seat pan is first raised and then lowered with respect to the seatframe during the simulated motion.
 19. A method of producing orenhancing a perceived sensation of motion according to any of claims 15to 18, wherein the motion(s) to be perceived by the user comprisetranslational (surge or sway) motions along or transverse to thedirection in which the user seated on the seat pan faces, and whereinthe perceived surge, including negative surge, motion is cued in theuser by movement of the seat pan along that axis and in the oppositedirection from that which is to be perceived by the user, and theperceived sway motion is cued in the user by movement of the seat pan ina direction transverse to that axis and in the opposite direction to thedirection of the sway motion that is to be perceived by the user.
 20. Amethod of producing or enhancing a perceived sensation of motionaccording to claim 19, characterised in that, the translational motionis accompanied simultaneously with pitch and/or roll motion.
 21. Amethod of producing or enhancing a perceived sensation of motionaccording to any one of claims 16 to 20, wherein the seat pan issimultaneously subjected to any two or more other motions selected frompitch, roll, heave, surge and sway.